1. Field of the Invention
The present invention relates to an optical device (for example, a display device for conducting display of numerical figures or letters or X-Y matrix display, and a filter capable of controlling light reflectance or light transmittance in a visible light region (wavelength: 400 to 700 nm)), as well as an electrolytic solution used for the device.
2. Description of the Related Art
Heretofore, electrochromic materials (hereinafter sometimes referred to as EC materials) have been used for voltage driving type display devices and adopted, for example, in digital clocks and the like for time display,
The electrochromic display device (hereinafter sometimes referred to as ECD) is a non-light emitting type display device and since it conducts display by reflection light or transmission light, it has an advantageous merit of reducing feeling of fatigue even after long time observation, as well as an advantageous merit such as relatively low driving voltage which reduces power consumption. For example, as disclosed in Japanese Patent Laid-Open Sho 59-24879, a liquid type ECD using, as the EC material, a biologen molecule derivative of an organic molecular type of providing colored and discolored states reversibly.
Along with development of precise optical instruments, light amount controlling devices which are fine in the size and consume less electric low power are required for replacing existent variable ND filters, and it becomes necessary to study if the ECD described above or techniques relevant thereto are adaptable or not.
However, in a case of utilizing the EC material, for example, the viologen molecule derivative to the ECD, there has been a problem in the response speed required actually and the shield performance and it has been difficult to put the material to practical use.
In view of the above, an electrochemical light controlling device using deposition/dissolution of silver has been developed in place of ECD taking notice on a transmitting type or reflection type light controlling device utilizing deposition/dissolution of a metal salt.
However, in the electrochemical light controlling device described above, while aimed values can be obtained for the response speed and the light shielding performance, a transparent electrode as a substrate (that is, a working electrode) tends to suffer from degradation and the working life as a device is short.
Particularly, since an overvoltage is applied to an ITO (indium tin oxide) electrode upon deposition and dissolution of silver, the electrode is liable to be damaged.